Communication and
Homeostasis
A2 Biology F214
Why do multi cellular organisms need
communication systems?
• Organisms need to
detect changes in their
external environment
eg: pressure on skin,
light, sounds,
temperature, chemicals
etc. The receptor cells
need to signal these
changes to the organism
so it can respond and
maintain its safety.
Why do multi cellular organisms need
communication systems?
Organisms need to detect
changes in internal
environments such as
temp, pH, water potential
of blood , tissue fluid, level
of toxins, etc as these can
affect the ability of cells to
function efficiently.
Enzymes, dehydration, lack of
respiratory substrate,
toxins inhibiting
metabolism, etc.
Why do multi cellular organisms need
communication systems?
• Organs work together to
maintain a constant
internal environment with
different organs having
different functions. These
functions have to be coordinated to keep the
environment constant
(Homeostasis)
• Pancreas, liver, muscles,
digestive system organs
are all used to maintain
blood glucose levels.
Why do multi cellular organisms need
communication systems?
• Cell Signalling: one cell
releases a chemical that
is detected by another
cell. The second cell
may respond to the
chemical signal in any
of a large number of
ways depending on the
type of cell and the
chemical stimulus
recieved.
• Cells signal using
hormones (the
Endocrine system) that
travel in the blood
stream and are picked
up by their target cells.
The endocrine system
enables long-term
responses.
Why do multi cellular organisms need
communication systems?
• Nerve impulses are
transmitted by neurone
networks across
synapses using
neurotransmitters. This
allows fast signalling
and responses to
rapidly changing
stimuli.
Homeostasis
•What does it
mean?
Homeostasis
• A system of monitoring
and adjustment to keep
conditions within safe
limits
Homeostasis
Monitoring
Controlling
Internal
conditions
To keep them
constant (or
within safe limits)
Despite external
changes
Egs
• temperature
• blood glucose levels
• blood salt concentration
• relative water potential of
blood, tissue fluid and cells,
• pH
• Blood pressure
• CO2 levels
Negative Feedback
Can you complete this with some real
life examples?
Positive Feedback
Can you complete this with some real
life examples?
Maintaining Body Temperature
• Describe the physiological and behavioural
responses that maintain a constant core body
temperature in ECTOTHERMS.
(What is an ECTOTHERM?)
• Describe the physiological and behavioural
responses that maintain a constant core body
temperature in ENDOTHERMS, with reference to
peripheral temperature receptors, hypothalamus
and effectors in skin and muscles.
(What is an ENDOTHERM?)
Maintaining temperature in
ECTOTHERMS
Think of some ways these animals
may be able to regulate their
body temperature
Control of temperature
• Ectotherms
• Seek sun or shade
depending on outside
temperature
• Expose more or less body
surface to sun
• Alter body shape to
change surface area
• Increase breathing
movements to evaporate
more water
Maintaining temperature in
ENDOTHERMS
Think of some ways these animals
may be able to regulate their
body temperature
Control of temperature
•
•
•
•
•
•
•
•
•
•
Endotherms
Sweating
Panting
Piloerection
Vasodilation
/vasoconstriction
Metabolic rate in liver
Shivering
Seek sun or shade
Alter orientation of body
Alter activity level
Diagram to
show changes
to skin surface
blood vessels
in warm and
cold
conditions.
Sensory Receptors and Nerve
Impulses
Learning Outcome 1
• Outline the roles of sensory receptors in
mammals in converting different forms
of energy into nerve impulses
What is a transducer?
• A cell that transforms one type of energy into
another
• Each type of transducer detects changes in a
particular form of energy (the stimulus)
• Although receptors detect changes in
different stimuli the receptor always converts
this change to electrical energy known as a
nerve impulse
Sense organs, receptors and stimuli
Sense Organ
Eye
Nose
Tongue
Skin
Ear
Muscle
Type of receptor
What does it detect?
Sense organs, Sensory Receptors
and Stimuli
Eye
Rods and cones (light sensitive
cells)
Light intensity (rods) and
wavelength (cones)
Nose
Olfactory cells lining inner surface
of nasal cavity
Presence of volatile
chemicals
Taste buds in tongue, hard palate,
epiglottis and first part of
oesophagus
Presence of soluble
chemicals
Pressure on skin
Skin
Pacinian corpuscles (pressure
receptors)
Ear
Sound receptors in cochlea (inner
ear)
Vibrations in air
Proprioceptors (stretch detectors)
Length of muscle fibres
Tongue
Muscle
Learning outcome 2
• Describe with the aid of diagrams
the structure & functions of sensory
& motor neurones
Structure
of
neurones
Sensory and Motor neurones
Node of
Ranvier
Axon terminal
Myelin sheath
Made of Schwann cells
Axon terminal
The Myelin Sheath
Diagram of the process of myelination of an axon. Myelination begins with the
invaginations of a single nerve axon into a Schwann cell; a mesoaxon is then formed.
As myelination proceeds, the mesoaxon rotates around the axon enveloping it in
concentric layers of Schwann cell cytoplasm and plasma membrane which contain high
levels of electrically insulating lipid
Electron micrograph of myelinated
neurone (cross section)
• l
neurone
Layers of
Schwann Cell
cytoplasm
and membrane
Learning outcome 3
• Describe and explain how resting
potential is established and
maintained
Establishing the “Resting Potential”
• At rest, the inside of a neuron's
membrane has a negative charge
(resting potential).
• As the figure shows, a Na+ / K+ pump
in the cell membrane pumps 3 sodium
ions out of the cell and 2 potassium
ions into it using ATP. (Type of transport?)
• However, because the cell membrane
is a bit leakier to potassium than it is
to sodium, more potassium ions leak
out of the cell. (Type of transport?)
• There are also many organic anions
(-ve charged) in the cytoplasm
• As a result, the inside of the
membrane builds up a net negative
charge relative to the outside. (-70mV
is the resting potential, the cell is
“polarised”
Sodium – Potassium
pump online tutorial
http://highered.mcgrawhill.com/sites/0072
495855/student_view0/chapter3/animatio
n__sodiumpotassium_exchange_pump__quiz_1
• Describe and explain how an action
potential is generated
• In all receptors changes in the level of the stimulus
(changes in energy levels) result in changes in
permeability of the membrane to Na and K ions
35
Small stimuli don’t cause a big enough
change in p.d. to generate an action
potential.
(P.d. doesn’t reach generator potential.)
Generating an Action Potential
• Stimulation of the receptor
causes Na+ channels to
open. The bigger the
stimulus the more
channels open.
• Na+ ions diffuse into cell
lowering potential
difference
• This makes even more
channels open (positive
feedback)
• When potential difference
reaches threshold (-50mV)
the voltage gated Na+
channels open
Generating an Action Potential (2)
• As more Na ions flood in
the potential difference
across the membrane
changes to +40mV
• Voltage gated K channels
open and Na channels
close (2&3)
• K ions diffuse out of cell
repolarising the cell (4)
• So many ions diffuse out
that the cell is
hyperpolarised (5)
• The Na/K pump reestablishes the resting
potential (6)
Local Current
Transmission of Action Potentials
in myelinated neurones (Saltatory conduction)
3
•
•
•
•
•
AP at 1 causes Na ions to move into axon
Na ions diffuse to areas of –ve charge further down axon towards 2
Voltage gated Na channels are only present at Nodes of Ranvier
So new AP starts at 3 and so on
The impulse moves in one direction only as it takes time to re-establish
distribution of ions using the Na/K pump.
• So the neurone cannot depolarise again immediately in that region
(refractory period)
Transmission of Action Potentials
in myelinated neurones (Saltatory conduction)
Describe, with the aid of diagrams, the structure of a cholinergic synapse.
The Synaptic Knob of Pre-synaptic Neurone
Post synaptic membrane
The postsynaptic membrane with a sodium ion channel and sodium ion
channel opened by acetylcholine
Outline the role of neurotransmitters in the
transmission of action potentials.
• Outline the roles of synapses
in the nervous system.
These EPSPs do not reach
the threshold potential
But when several are added
together sufficient Na
ions have entered the cell to
initiate a new action
potential
Extension:
Animation showing the linking of an
action potential to muscle
movement
http://www.youtube.com/watch?v=70DyJ
wwFnkU&feature=PlayList&p=80C4BB587
45CB30E&index=17
Animation to explain a
synapse
http://www.youtube.com/watch?v=HXx
9qlJetSU&feature=PlayList&p=80C4BB5
8745CB30E&index=29
Use your new knowledge to create a
script to describe and explain the
following animation:
http://www.youtube.com/watch?v=90cj4
NX87Yk&feature=PlayList&p=80C4BB58
745CB30E&index=24
Compare and contrast the structure and function
of myelinated and non-myelinated neurones.
•
Outline the significance of the frequency
of impulse transmission.